3D Stereo - Saving both Left and Right render images
If you want to save the render result you can simply use the keyword argument write_still = True.

The saved image will conform to your view format settings in the render options panel. If you set the view format to Individual, the following lines will save two images named render_L.png and render_R.png.

bpy.data.scenes['Scene'].render.filepath = 'D:\\render.png'
bpy.ops.render.render(write_still=True)